This application relates to a retention feature for retaining a thrust washer against rotation in a planetary gear system.
Planetary gear systems are well known, and have been utilized to provide a gear change between an input and an output. A sun gear rotates about a central axis, and a ring gear rotates about the same center but outwardly of the sun gear. A plurality of planet gears are positioned to transmit rotation from the sun gear to the ring gear.
In one known type of planetary gear system, the planet gears are mounted on stationary shafts positioned inwardly of the ring gears. The planet shaft provides an inner race for bearings which support the planet gears. Also, thrust washers sit at both ends of the planet shaft, and provide axial thrust surfaces against the end surfaces of the planet gears.
One application of a planetary gear system is in an air turbine starter system. In an air turbine starter system, air is delivered across a turbine rotor to drive the rotor. The rotor drives a sun gear, which drives a ring gear through planet gears. The ring gear in turn drives a starter output shaft for a gas turbine engine.
In such applications, the asymmetry and clearances of the planet gears tend to induce an axial force, which reacts against the thrust washers. Those reacted gear forces attempt to rotate the thrust washers, which must remain stationary relative to the fixed housing. The thrust washers serve to provide a designated durable surface for that relative motion and loading. In the prior art, the thrust washers received a simple pin to limit rotation.